I discovered platinum-palladium printing in the early 1990s with the last ready-made paper manufactured by The Palladio Company, Inc that I had ordered from the United States. It took me just long enough to get the hang of it, and by the time I wanted to use this process to make the prints for the ‘Histoires de pierre’ series, production had ceased. The big companies like Kodak and Ilford had already stopped all production between the two world wars. So we had to learn how to prepare the emulsion ourselves, find the chemicals and test the papers that were currently chemically compatible with the process. This was made all the more difficult by the fact that, at the time, internet usage was nothing like it is today. The process is not new, however, having been developed by William Willis, son of a famous English engraver, who filed three successive patents: English patents of 5 June 1873, 20 August 1878 and 15 August 1880.

The platinum and palladium salts used are not very sensitive to light, so it is necessary to use a more photosensitive chemical reagent. Ferric oxalate is most often used. Exposed to UV light, the iron salt is reduced and produces a faintly visible image formed by ferrous oxalate, which has the property of decomposing platinum/palladium salts, forming a metallic black precipitate as soon as it comes into contact with a developer, potassium oxalate, for example. Light does not therefore act directly on the metal salts. Development transforms the image formed into a platinum/palladium image. This print is an entirely hand-made object, from the manufacture of the emulsion to its coating with a brush on very fine paper, usually handmade.